1. Field of the Invention
This invention relates generally to the manufacture of high performance semiconductor integrated devices. More specifically, this invention relates to the process quality control utilized during the manufacture of high performance semiconductor integrated devices. Even more specifically, this invention relates to a process quality control that uses previous scan data to more efficiently utilize quality control equipment.
2. Discussion of the Related Art
In the manufacture of high performance semiconductor integrated devices there are several tradeoffs that must be made. One of the tradeoffs is the tradeoff between tight control of process quality control and high volume production. As can be appreciated, inspecting every device on every wafer after each process step would effect the highest quality control. However, as can also be appreciated, the inspection of every device on every wafer after each process step would be highly detrimental to the goal of high volume production. The typical tradeoff is to perform inspections of random samples selected after various steps throughout the entire manufacturing process.
A typical tradeoff in a quality control process is to select one or more wafers from each manufacturing lot. A manufacturing lot is typically the number of wafers in a cassette and the typical cassette contains about 24-25 wafers. As the size of wafers increases and as the number of die on each wafer increases, the time required for scanning and inspecting each die on the selected wafer or wafers also increases. In addition, as the size of each die shrinks, the number and kind of defects that can affect the operation of the die have also increased. The increase in the number and kind of defects that must be detected and classified has also increased the time required for scanning and inspecting each die on the selected wafer or wafers. The increase in time and complexity of the quality control process is better understood when it is realized that a typical production cycle of product wafers, the selected wafers may be scanned as many as 40 times or more during a typical manufacturing process.
The scanned data is usually saved to a relational database for further post-inspection review and/or evaluation, but unfortunately, the results of previous scans of the current wafer being processed are usually not available to the tool doing the current scan or to the operator monitoring the current scan. The scanned data includes many defect classifications and defect data, including defective die levels, defect sizing data and types of defects, which could lead to using a different type of scan or even rejecting the proposed wafer in lieu of another wafer from the same lot which might be more indicative of the current process trend.
Therefore, what is needed is a quality control process that reviews previous scan data, both for previous lots and for the current lot, and that uses that scan data to optimize equipment performance.